Hi, we've been to AGP Chicago twice now. I would also recommend either the lunch or dinner. They are both well worth the price. We actually had leftovers to take with us. AG makes it a cute experience for the girls.
We also enjoyed the theater experience. We are theater goers but I had my doubts about an "American Girl" play. However, I was pleasantly surprised by the professionalism of the performance.
The last time we went we actually scheduled a 2:00 play time and a 5:00 dinner time. We were able to enjoy some of Chicago's sites before arriving at AGP around 1:00. After we exited dinner the photography studio had absolutly no line and the store was not as busy.
Hope that helps.